PROJECT SUMMARY The worldwide incidence of obesity and type II diabetes has risen alarmingly over the past few decades. The World Health Organization now estimates that 347 million people are diabetic, and that diabetes- related deaths will rise by 50% over the next 10 years, making it the 7th leading cause of death.1 A hallmark of diabetes is pancreatic beta cell failure, wherein beta cells are unable to secrete enough insulin to maintain normoglycemia. Many mechanisms have been suggested as the cause of this failure, but more recently, dedifferentiation has been identified as a common pathogenic mechanism in murine, primate, and human diabetes. Targeting dedifferentiation as a therapeutic measure is particularly attractive since dedifferentiating beta cells should theoretically be amenable to ?redifferentiation.? However, the causes of dedifferentiation remain unknown. The proposed project seeks to examine whether cytochrome b5 reductase isoform 3 (Cyb5r3) can play a role in this process. Cyb5r3 was identified as a differentially expressed transcript in dedifferentiating beta cells. Moreover, loss of Cyb5r3 was specifically linked to decreased FoxO1 function, a hallmark of beta cell dedifferentiation. Finally, loss of the related isoform Cyb5r4 in mice is known to cause early-onset diabetes independent of insulin resistance. My preliminary work has already established that Cyb5r3 is a direct transcriptional target of FoxO1, and that it is required for the maintenance of mitochondrial basal respiration and glucose-stimulated insulin secretion in vitro. I hypothesize that Cyb5r3 is critical to normal beta cell function in vivo, and that its loss contributes to beta cell dedifferentiation. I will therefore describe two Specific Aims that seek to further characterize the role of Cyb5r3 in beta cells. First, I propose to corroborate my preliminary data by establishing a Cyb5r3 gain-of-function model, which I predict will partially reverse insulin secretory defects in diabetic mouse islets. I will also study how Cyb5r3 loss-of-function impairs mitochondrial respiration and insulin secretion by examining mitochondrial complex function. Second, I am generating mice lacking Cyb5r3 specifically in beta cells, a model I have termed ?B-Cyb5r3.? The B-Cyb5r3 mice will undergo thorough metabolic phenotyping (e.g. glucose and insulin tolerance tests, hyperglycemic clamp studies), as well as histopathological and functional assessment of islets and beta cells, which we expect will reveal a beta cell-specific defect in insulin secretion. In summary, this comprehensive set of experiments will not only contribute significantly to my development as a scientist but may also prove valuable to the treatment of diabetes.